1. Field of the Invention
The present invention relates to technical concept applicable without changing an existing network as a transmission and reception technology operable in circumstances of a low signal to noise ratio (SNR) to an existing satellite communication network.
2. Description of the Related Art
A conventional digital video broadcasting-satellite-second generation (DVB-S2) transmission system may perform transmission suitable for a channel environment in which a signal to noise ratio (SNR) ranges from −2.35 decibels (dB) to about 16 dB. However, in a case of satellite communication, an extremely low SNR may occur due to a rainfall environment and a difficulty in installation of an antenna, and a mobile terminal may have an interference effect on an adjacent channel due to an antenna pointing error when a signal with a high SNR is transmitted. Accordingly, when a satellite signal is received and transmitted, the signal is to be transmitted in an environment of an extremely low SNR. In a case of currently used DVB-S2 standards, since a great number of transceivers are already installed, performing a new framework may be impossible. Accordingly, a frame is to be configured to not affect existing equipment.
As one associated technology, a band spread technology may be expected. A conventional band spread technology requires a separate device for a band spread function and thus, a receiver in which the band spread function is not supported may have a difficulty in receiving data.
In general, satellite communication is operated with a fixed bandwidth. The band spread technology refers to a technology that spreads a bandwidth of a signal to transmit low signal power. Among various methods of spreading a bandwidth, a relatively simple method may be a technology that increases an intensity of a signal by transmitting identical data repeatedly and combining such data at a reception end.
Accordingly, in order to use the general band spread technology and other technologies, simultaneously, an amount of data of a signal of which a band is to be spread in a fixed bandwidth may be reduced. In this example, when the amount of the data is reduced due to a form of DVB-S2, a number of dummy frames may be generated. Based on such concept, the dummy frames may be replaced with a form in which an existing signal frame repeats.
In general, the band spread technology may expect a symbol replica technology of a time domain, a frame replica technology, and a frequency replica technology.
In the frequency replica technology, a non-linear amplifier may be used for satellite communication. Accordingly, intermodulation distortion may occur and thus, it may be difficult to apply a multicarrier technology.
The symbol replica technology has been known as a direct sequence band spread. However, a conventional DVB-S2 receiver may be unable to receive a signal of such a waveform.
In a case of the frame replica technology, reception may be impossible in an environment of a low SNR.
When reception signals are accumulated synchronously, such reception may be possible. However, in a case of an adaptive coding and modulation (ACM) technology of DVB-S2, a length of a frame may differ and thus, synchronous accumulation may be impossible.
When communication is performed in a conventional environment of a low SNR, transmission may be possible through symbol replica or channel encoding. In a case of the symbol replica, a scrambling process may be performed in order to guarantee a spectral flatness. A simple implementation may be possible by performing a process of accumulating repeated symbols. The channel encoding technology may be the most robust technology for increasing performance in an environment of a low SNR. However, when a carrier recovery is impossible due to a low intensity of a reception signal, the channel encoding technology may be inapplicable.
The foregoing two technologies may be implemented readily using a conventional narrow band or wide band service. However, the two technologies may be difficult to apply while maintaining a coexistence with the conventional service.
When the two technologies are applied, a separate network may be necessary and thus, an issue of backward compatibility with respect to an existing user may arise. An issue may be resolved by introducing the frame replica technology into a modulation and demodulation method for satellite communication having a wide-ranging SNR.